Analog to digital converters, ADCs, are used to convert signals from the real world to the digital domain, the signals being obtained from, for example, cameras, microphones, temperature sensors, pressure sensors, position transducers, gas-flow sensors, electro-chemical cells (e.g., for blood glucose monitoring), and many other forms of transducer. Those real world measurements are converted into digital values that can be processed by computers, micro-processors, and the like.
Parameters of ADCs include how fast they are, how finely they can distinguish changes in the input signal (i.e., their resolution), and how linear they are. Ideally, all single bit transitions in the output word of an ADC would equate to a fixed size transition in the analog input signal presented to the ADC. In reality, this is very hard to achieve.
Non-linearity in an analog to digital converter can be improved by dithering the ADC. In effect, a non-linearity is smeared out over several digital codes of the ADC by the application of the dither, thereby reducing the severity of the non-linearity at any given ADC output code. The dither value can then be subtracted such that the digital value of the ADC output signal (the conversion result) is not affected by the dither, but the performance of the ADC is improved.
As noted above, speed is one of the parameters of the ADC. To increase the conversion rate, the task of converting a signal may be shared between two or more series connected stages. Such an arrangement is known as a pipeline. A stage of a pipeline performs part of the analog to digital conversion. A stage may also form a residue, which represents a difference between the analog signal the stage received and the analog value equivalent to digital conversion result of the stage. The residue is passed to a subsequent stage of the pipeline. The subsequent stage performs an analog to digital conversion of the residue.